As semiconductor device geometries continue to decrease, the importance of ultra clean processing increases. Aqueous cleaning within a tank of fluid (or a bath) followed by a rinsing bath (e.g., within a separate tank, or by replacing the cleaning tank fluid) achieves desirable cleaning levels. After removal from the rinsing bath, absent use of a drying apparatus, the bath fluid would evaporate from the substrate's surface causing streaking, spotting and/or leaving bath residue on the surface of the substrate. Such streaking, spotting and residue can cause subsequent device failure. Accordingly, much attention has been directed to improved methods for drying a substrate as it is removed from an aqueous bath.
A method known as Marangoni drying creates a surface tension gradient to induce bath fluid to flow from the substrate in a manner that leaves the substrate virtually free of bath fluid, and thus avoids streaking, spotting and residue marks. Marangoni drying uses relatively small amounts of IPA. Specifically, during Marangoni drying a solvent miscible with the bath fluid is introduced to a fluid meniscus which forms as the substrate is lifted from the bath or as the bath fluid is drained past the substrate. The solvent vapor is absorbed along the surface of the fluid, with the concentration of the absorbed vapor being higher at the tip of the meniscus. The higher concentration of absorbed vapor causes surface tension to be lower at the tip of the meniscus than in the bulk of the bath fluid, causing bath fluid to flow from the drying meniscus toward the bulk bath fluid. Such a flow is known as a “Marangoni” flow, and can be employed to achieve substrate drying without leaving streaks, spotting or bath residue on the substrate.
A conventional Marangoni drying system is disclosed in European Application number 0 385 536 A1, titled “Method and Arrangement for Drying Substrates After Treatment In a Liquid.” The '536 System submerges a substrate in a fluid bath. A vapor (e.g., an alcohol vapor) miscible with the bath fluid is mixed with a carrier gas and then passed over the surface of the fluid bath via a plurality of nozzles. The vapor mixes with the fluid bath along the surface thereof, lowering the surface tension of the fluid bath. A fluid meniscus forms along the air/liquid/substrate interface as a substrate is lifted from the fluid bath. This meniscus is formed from the surface layer, and thus has a lower surface tension than does the bulk bath fluid. Accordingly, fluid flows from the surface of the substrate to the bulk bath fluid, leaving a dry substrate surface. Although apparatuses such as that disclosed in the '536 Application effectively remove fluid from the substrate, they consume a considerable amount of fluid because the bath fluid cannot be filtered and recirculated to remove drying vapor therefrom. Thus, the bath fluid must be replaced frequently to maintain a sufficient surface tension gradient at the drying meniscus. Further, considerable time is required to transfer a substrate from the cleaning to the rinsing bath, or to replace bath fluid.
Accordingly, a need exists for an improved method and apparatus that quickly and effectively cleans, rinses and dries a substrate, eliminating not only streaks, spotting and bath residue marks, but also conserving rinsing fluid consumption and reducing the overall time required for the cleaning, rinsing and drying process.